photocell sensor connection with magnetic contactor
Photocells
A photocell is a light-to-electrical transducer, and there are many different types available. Light is an electromagnetic radiation of the same kind as radio waves, but with a very much shorter wavelength and hence a much higher frequency.
Light radiation carries energy, and the amount of energy carried depends on the square of the amplitude of the wave. In addition, the unit energy depends on the frequency of the wave.
The sensitivity of photocells can be quoted in either of two ways, either as the electrical output at a given illumination, using illumination figures in units of lux, often 50 lux and 1000 lux, or as a figure of power falling on the cell per square centimetre of sensitive area, a quantity known as irradiance. The lux figures for illumination are those obtained by using photometers, and a figure of 50 lux corresponds to a ‘normal’ domestic lighting level good enough for reading a newspaper. A value of 1000 lux is the level of illumination required for close inspection work and the reading of fine print; on this scale, direct sunlight registers at about 100 000 lux. The use of milliwatts per square centimetre looks more comprehensible to anyone brought up with electronics, but there is no simple direct conversion between power per square centimetre and lux unless other quantities such as spectral composition (colour balance) of light are maintained constant. For the range of wavelengths used in photocells, however, you will often see the approximate figure of 1 mW/cm2 = 200 lux used.
Another important point relating to the use of photocells is that they are not uniformly sensitive at all visible colours.
For many types of sensors, the peak sensitivity may be at either the red or the violet end of the visible spectrum, and some sensors will have their peak response for invisible radiation either in the infrared or the ultraviolet. A few devices, notably some silicon photodiodes, have their peak sensitivity for the same colour as the peak sensitivity of the human eye.
The main classes of photocells are photoresistors, photovoltaic materials, and photoemitters.
photocell sensor connection with magnetic contactor
Photocells
A photocell is a light-to-electrical transducer, and there are many different types available. Light is an electromagnetic radiation of the same kind as radio waves, but with a very much shorter wavelength and hence a much higher frequency.
Light radiation carries energy, and the amount of energy carried depends on the square of the amplitude of the wave. In addition, the unit energy depends on the frequency of the wave.
The sensitivity of photocells can be quoted in either of two ways, either as the electrical output at a given illumination, using illumination figures in units of lux, often 50 lux and 1000 lux, or as a figure of power falling on the cell per square centimetre of sensitive area, a quantity known as irradiance. The lux figures for illumination are those obtained by using photometers, and a figure of 50 lux corresponds to a ‘normal’ domestic lighting level good enough for reading a newspaper. A value of 1000 lux is the level of illumination required for close inspection work and the reading of fine print; on this scale, direct sunlight registers at about 100 000 lux. The use of milliwatts per square centimetre looks more comprehensible to anyone brought up with electronics, but there is no simple direct conversion between power per square centimetre and lux unless other quantities such as spectral composition (colour balance) of light are maintained constant. For the range of wavelengths used in photocells, however, you will often see the approximate figure of 1 mW/cm2 = 200 lux used.
Another important point relating to the use of photocells is that they are not uniformly sensitive at all visible colours.
For many types of sensors, the peak sensitivity may be at either the red or the violet end of the visible spectrum, and some sensors will have their peak response for invisible radiation either in the infrared or the ultraviolet. A few devices, notably some silicon photodiodes, have their peak sensitivity for the same colour as the peak sensitivity of the human eye.
The main classes of photocells are photoresistors, photovoltaic materials, and photoemitters.
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